What can we say about the effect of the same-sex marriage issue on the election? That will likely clarify a bit as analysts pour over the results, but I suspect the key lesson is this: the marriage issue can magnify turnout among those already disposed to support Republicans, but it cannot buck a national electoral tide. And the degree to which same-sex marriage gets linked to a particular race depends on many things, from how much the candidate says about the issue, to the salience of other controversies in the campaign.

Take Virginia. The marriage amendment seems to have boosted turnout in Virginia, and may actually have helped Allen stay as close to Webb as he did. On the other hand, as Bill Kristol said last night, Allen focused his campaign on personal attacks, and actually missed the opportunity to say more about the marriage issue. That made it easier for voters to separate their support for the marriage amendment from their vote for senate.

In New Jersey, Kean lost to Menendez, and by a larger margin than he was trailing in the polls when the New Jersey Supreme Court’s decision was made. By itself, that might have sent a signal to the New Jersey state legislature that the public was comfortable with same-sex marriage. Yet polling since the New Jersey decision shows that this is clearly not the case.

Public support for same-sex marriage is, if anything, down in New Jersey. So again, we’ve seen a relative detachment between public sentiment on the marriage issue and votes for congressional candidates, in a year when other issues pushed the trend against the Republicans.

In short, the lesson is that the marriage issue, by itself, isn’t enough to turn around a national election in a year when big controversies like the war dominate. Yet it does seem that marriage amendments boost turnout. In a year when big winds aren’t blowing against Republicans, that would likely still make a significant difference. We also need to remember that Massachusetts imposed full-scale same-sex marriage, while New Jersey’s court went for civil unions. Had New Jersey gone all the way, the political effect would no doubt have been significantly greater.